Heat-treating method



Aug. 17, 1943.; R. 0. DAY

HEAT TREAT ING METHOD Original Filedoct. '16, 1957 2 Shets-Sheet i INVENTOR ROGER 0. DAY

ATTO RNEY Aug. 17, 1943. R. 0. DAY

HEAT TREATING METHOD Original Filed Oct. 16, 1937 2 Sheets-Sheet 2 INVEINTOR ROGER 0. DAY

ATTORNEY Patented Aug. 17, 1943 HEAT-TREATING METHOD Roger 0. Day, Westfield, N. l, assignor to The Linde Air Ohio Products Company, a corporation of Original application October 16, 1937, Serial No.

169,373. Divided and this application July .30, 1940, Serial No. 348,331

Claims.

Thls invention relates to the heat treatment or hardening of metal articles, and specifically to a method of hardening a ferrous metal article in which a surface thereof is to be heated uniformly to a desired temperature. This inverition is of particular value in the heat treatment or surface hardening of articles such as gearteeth and the like, wherein the article tends to conduct a greater amount of heat from certain portions than from other portions of the surface to be treated. This application is a division of my application Serial No. 169,373, filed October 16, 1937, now United States No. 2,224,006.

Heretofore, gear teeth have been hardened by utilizing a single blowpipe, usually an ordinary welding blowpipe, but the heat applied therefrom cannot be accurately controlled to obtain a uniform heating effect over the surface of the tooth and retain a tough, unhardened core of the most desirable shape. A nonuniformity of heating results in non-uniformity of hardening,.with the result that a greater amount of wear will occur at some points, such as adjacent the'root, than at others, such as adjacent the top. Furthermore, if a single blow I pipe flame is applied to the surface of a gear -tooth adjacent the pitch circle, the hardened portion usually extends into the tooth for a considerable distance, and reduces the crosssectional area of the tough, unhardened core to such an extent that the core at that point is not well adapted to resist impact and shock. Moreover, if a single-blowpipe flame is applied to the face of the tooth, i. e. at a point closer to the top of the tooth or top land," an overheating of the top results, and internal strains and a considerable decrease in ductility result,

thereby producing a tendency for the tooth to chip or crack.

The principal objects of this invention are to provide a method of hardening a gear tooth to produce hardened surfaces and a tough, unhardened core and top; to provide a method of heat-treating gear teeth or other metal articles in which a surface portion to be hardened is heated and quenched uniformly; to provide such a method of heat-treating gear teeth in which the opposite surfaces of a single tooth may be hardened simultaneously; and to provide a method of heat treating gear teeth and other metal articles in which a surface'portion is heated by a plurality of heating flames, the distribution of the heating flames being so controlled that the surface portion is heated uniformly. Other objects and novel features of this invention will become apparent from the following description and accompanying drawings, in which:

Fig. 1 is a, partial end view of a gear and apparatus adapted to carry out the method of this invention, illustrating the heat-treatment of the surfaces of a gear teeth;

Fig. 2 is a front view of a blowpipe head of the apparatus of Fig. 1;

Figs. 3 and 4 are vertical sectional views taken along the. lines' 3-3 and 4-4, respectively, of

Fig. 5 is a horizontal sectional view taken along the line 5-5 of Fig. 2;

Fig. 6 is a cross-sectional view of a gear tooth V heat-treated in accordance with the principles of this invention;

Figs. '7, 8, and 9 are front views, partially in section,"of alternative forms of blowpipe heads;

the top of the tooth; the portions of the surfaces closely adjacent the top of the tooth are preferably heated only by conduction from the portions of the surfaces remote therefrom; and the top of the tooth, or top land," is preferably heated insufficiently to produce hardening thereof. The surfaces are also preferably so heated that .the hardened portion extends from the top to the root of the tooth, each hardened portion preferably being deepest adjacent the pitch circle or pitch line and progressively shallower along the face and flank towards the top androot of the tooth, respectively; but a tough, unhardened core is retained which has a crosssectlonal area in a plane adjacent the pitch line usually no smaller than, and preferably substantially the same as, its cross-sectional area adjacent the top of the tooth.

Generally, in accordance with this invention, a longitudinally extending surface of a metal body or article such as a gear tooth-and which body or article tends to conduct different amounts of heat from transverse portions of the surface is hardened by applying thereto a plurality'of high temperature heating flames having individually substantially the same heating effect but the distance between the flames is varied in' accordance with the tendency for heat to be conducted away from the various portions of the surface, so that a greater number of heating flames are directed against those portions of said surface from which a greater amount of heat tends to be conducted. The

heating flames are preferably disposed in one or more rows extending transversely of such surface. The heating flames in each row may be disposed more closely together at one end of each row, such as adjacent the root of the gear tooth, and at successively increasing distances apart to the other end of each row, or

' out by the apparatus illustrated-in Fig. 1, in

which two blowpipe heads H and H areutilized in hardening the surfaces of a tooth T of a gear G. The blowpipe heads H and H are substantially identical in construction exceptthat the relative positions of the parts are transposed so thaLgne is right hand and the other is left hand; and they receive a combustible mixture, such as a mixture of oxygen and acetylene, through conduits l5 and I6, respectively, which are suitably connected to the bodies or handles l1 and iii of conventional oxy-acetylene blowpipes provided with valves V for controlling the flow and proportions of the combustible mixture. The heads H and H receive a cooling and quenching medium, such as water, through conduits i9 and 20, respectively-the cooling medium being utilized also as a quenching medium to provide a more compact construction.

The blowpipes and heads are supported in operative relation with respect-to the tooth T by a suitable holder which includes a slotted horizontal arm 2! secured to a rod 22. The head H is-adjustable horizontally through a slotted vertical arm 23, slidable horizontally upon the arm 2!. and adapted to be clamped at any desired point along the arm 2! by 'a. bolt 24 and nut 25; and is adjustable vertically through a slide 26, slidable vertically along the arm 23 and adapted to be secured at any desired point along the arm 23 by suitable means similar to'the bolt 24 and nut 25. 'The head- H is angularly adjustable through a clamp 21, within which the blowpipe body it is secured, and which is pivotally mount- .so that vertical and horizontal adjustments of the blowpipes and heads as a unit with respect to the gear.,G and tooth T may be effected.

The right hand head H, shown in Figs. 3 to 6,

is provided with a surface 30 which is inclined to the sides of the head and forms one surface of a lower portion 3!, which forms a lower end of reduced thickness and permits the head to be inserted between two closely spaced gear teeth. The head H is also provided with an inlet 32 to which the combustible mixture conduit l5 may be connected, and passages .33 and 34 which lead the combustible mixture to a distributing chamber 35 in the lower end of the head. A plurality of heating gas outlets 36 of substantially equal diameter lead from the chamber 35, terminating in the surface 30, and are preferably disposed in staggered relation in substantially vertical rows, so that the heating jets produced will tend to overlap and product a more even heating effect. The heating jets discharged from outlets 36 each have substantially-the same heating effect, taken individually, but the distance between centers of adjoining outlets 36, and consequently also the distance between adjoining heating jets or flames, increases progressively from the lower to the upper end of each row, so that closely adjoining heating jets will apply a greater amount of heat adjacent the root of the tooth and a progressively lesser amount upward- 1y towards the top of the tooth. The spacing of the outlets and heating flames compensates for the tendency for a greater amount of heat to be conducted from the root of the tooth into the body or hub of the gear, and results in a uniform heating of the wearing surface of the tooth. The principle of variation in spacing of heating flames of substantially equal heating effect may be utilized in other instances to provide uniform ed upon a fixed boss 28 which is in turn mounted H and H and gear G to prevent possible interference with the operation or view of the operation by the operator.

The heads H and H are moved across the heating of a surface or surface portion of a metal article. For instance, in hardening crankshaft bearings, in which the cheeks tend to conduct a greater amount of heat awayfrom each end of the bearing surface than is conducted away from flames spaced more closely together at each end of each row than at the center of each row.

lrvhen the bearing is rotated while heating flames disposed in the foregoing manner are directed against the surface thereof, or a relative movement between the heating flames and the surface of the bearing is efiected in any other manher, the surface of the bearing will be heated uniformly and all portions of the bearing surface. across the .width thereof, will reach the desired temperature simultaneously. I

Referring again to head H, the passage 34 may be disposed substantially perpendicularly to the chamber 35, so that the combustible mixture will not be projected directly into the upper of the outlets 36, and a uniform distribution of the combustible mixture to all of the outlets 36 will be obtained. The passage 33 may be drilled from the upper end of the head and the passage 3 2,326,840 from the surface 30, the ends of the passagesbeing closed by suitable means, such as plugs 31 which are secured in the ends of the passages in a suitable manner, such as by welding or brazing. The distributing chamber 35 may be formed by 'a suitable slot in the lower portion of the head, the

outer periphery of the slot being closed by a substantially U-shaped strip 3% secured to the head in a suitable manner, such as by welding or brazsurface 30 of the head, and are preferably. in-

clined rearwar'dly and away from the heating gas outlets, desirably at an angle of about. 30, so

that the quenching jets will not interfere with the heating flames. The quenching outlets 43 are also disposed in a plurality of rows so as to obtain complete quenching without splashing and interference with the heating flames. Inasmuch as the quenching outlets are inclined at an angle to the direct on in which the cooling and quenching fluid is discharged from the passage 4| into the chamber 42, it is unnecessary to provide a supplementary directing passage similar to the heating gas passage 34. The passage 8! and cham ber 42 may be drilled from the top of the head and lower portion 3|, and the open ends thereof closed by suitable means, such as plugs 54 which are secured therein ina-suitable manner, such as by welding or brazing.

During operation, the surface 39 is usually d sposed at an angle to the center line of the gear tooth so that the heating flames will be directed substant ally normally onto the surfaces of the tooth. For the larger sizes of gear teeth, this angle is preferably substant ally the pressure angle, whichis 14%) for involute teeth. In addition; the heads H and H are preferably so positioned with respect to the tooth T that the uppermost of the heating flames will impinge upon the faces at points which are spaced from. the

top of the tooth, so that the closely adjacent the top-w ll be heated by conduction only, and overheating of the same will'be avoided.

A heat treated gear tooth having hardened sectional areas of substantially the extent of portions 55 and of the tooth 6f Fi 6. usua ly will rtions of the faces larger than that adjacent the top; but in any event the cross-sectional area of the tough, unhardened core usually will not be substantially smaller adjacent the pitch circle than adjacent the top. I

The heads H and H are particularly adapted to be utilized in hardening the teeth of gears having a diametral pitch of about two.

teeth, such as those of gears havinga diametral pitch of one or less, is provided with an inclined surface and a lower portion 52 of larger extent than the surface and lower portion-3| of the head H. The head is also provided with a combustible mixture inlet 53 and passages 54 and 55 which lead the combustible mixture to a distributing chamber 56. Here, a plurality of heating gas outlets SIleading from the combus-,

tible mixture distributing chamber 56 and terminating in the inclined surface 5|, are greater in number and'extend over a greater .distance than the outlets of the head H in order to heat the surfaces of a larger tooth. As before, the heating gas outlets are disposed in vertical rows and ,in staggered relation so as to produce a-more even heating effect, and are spaced at increasing distances apart from the lower to the upper end of each row 50 as to produce a uniform heating effect upon the tooth:

The head 50 is also rovided with a cooling and quenching fluid in et 58 and a passage 59 which leads to adistribut'ing chamber 60, disposed alongside of the heating gas distributing chamber 58. Leading from the chamber 60 are a plurality of outlets 6l which are disposed in a plurality of vertical rowsand inclined rearwardly and away from the heating gas outlets in a manner similar to that previously described. Due to the increased size of the. tooth to be treated, and the cons quent increased size of the blow pipe head, the pa sage 56 may be formed by a hole drilled from the top of the lower por tion. 52 of the head 50, with the upper end thereof being'closed by a suitable plug, instead -of being formed by a slot as in the headH,- but be produced when the heads H and H' are moved across the width of the tooth Tein a direct on outwardly from the draw ngso as to heat and cool successive portions of the surfaces thereof. In such a tooth. the too or top .land of the tooth. such as the top 51 of the tooth of Fi 6. w ll. be unhardened; the hardened portions will be dee est adjacent the pitch circle or pitch line 48,

being progressively shallower fromthe pitch line along the flank, or portion below the pitch line, to the root, and also being progressively shallow- .in an inclined surface I2, are disposed in stag-" gered relation in alplurality of rows and also er from the pitch line-along the face, or portion above the pitch line, to the top of the. tooth; and a tough, unhardened core, such as the core 49 which has substantially the same cross-sect onal area in a plane adjacent the pitch circle 48 and adjacent the top 41, will be retained; In some instances, such as in the case of small gear teeth, the tough, unhardened corewillhave a cross-secthe method of construction of the head 50 is otherwise similar to that of the head H.

"For heat-treating teeth of smaller gears, such as those having a diametral pitchv of about three, blowpipe heads may be provided which are similar to head illustrated in Figs. 8 and 11.

The head .65, provided with a lower portion ,66'

which is thinner than the lower portion 3| of the head. H to permit insertion between more closely spaced gear teeth, is also provided with Q a combustible mixture inlet 61 and passages 68 and 89 leading to a combustible mixturedistributing chamber [0, from which heating gas outlets I! lead. The outlets H, lesser in number than the outlets of the head H and terminating are spaced from each other at increasing distances apart from the lower to the upper end of each row. The head 65 is also provided with a cooling and quenching fluid inlet I3 and a passage 14 which leads to a distributing chamber 16, disposed alongside of the heating gas jdistributingchamber i0. A plurality of quenching fluid outlets; 16 lead from the distributing chamber and terminate in the surface I2, the outlets being disposed in a plurality of vertical rows and preferably being inclined at an.angle rearwardly tional area adjacent the pitch circle slightly As shown in Figs. '7and 10, a, head 5% similar thereto but adapted to be utilized in hardening larger gear and away from the heating gas outlets, as pre viously described. The method of construction of the head 65 is similar to that of the head H.

For heat-treating still smaller teeth, such as those of gears having a diametral pitch of four or more, blowpipe heads may be provided which are similar to head 89, illustrated in Figs. 9 and 12. The head 80, provided with a lower portion 8| which is still thinnerthan the lower portion 31 of the head H, is also provided with a combustible mixture inlet 82 and passages 83 and 84 leading to a distributing chamber 85, from which heating gas outlets 86 lead. The heating gas outlets 86 are fewer in number than those of the heads previously described, but are similarly disposed in a plurality of vertical rows and in staggered relation, as well as being spaced at increasing distances apart from the lower to the upper end of each row. The head 80 is also provided with a cooling and quenching fluid inlet 81 and a passage 88 leading to a plurality of distributing chambers 89, from each of which a row of quenching outlets 90 lead. The outlets 90, as before, are preferably inclined at an angle rearwardly and away from the heating gas outlets. A plurality of distributing chambers 89 are utilized merely because of the smallness of the teeth to be treatedand the attendant diminishment in size of the. head, and the method of contruction of the head 80 is otherwise similar to that of the head H.

Although the method of this invention has been described particularly with reference to the heat treatment of gear teeth, it is to be understood that the principles of this invention may be applied to the heat-treatment of the teeth of worm gears or racks, of screw threads, or other projecting portions of metal articles. It is to be further understood that certain principles of this invention'may be utilized in the heat treatment of crankshaft bearings, as indicated, and

also in the heat treatment of other types of v number of heating flames are directed against those portionsof said surface from which a great- ,er amount of heat tends to be conducted.

. 2. A method of heat treating a surface of a metal article wherein said article tends to conduct different amounts of heat from transverse portions of said surface, such method comprising directing against said surface at least one row of high temperature heating flames extending transversely thereof, each of said heatin flames having individually substantially the same heating effect but the distance between adjoining flames in said row being yaried in accordance ,with the tendency for heat to be conducted from said surface, so that a greater number of heating flames are directed against theportions of said surface from which a greater amount of metal articles having surfaces which require a greater amount of heatover some portions of the surface than over others; and that various other changes may be made whichwill not depart from the spirit and scopeof this invention.

-What is claimed is:

1. A method of heat treating a surface of a metal article wherein said article tends to conheating effect but the distance between said flames being varied in accordance with thetend- -ency for heat to be conductedaway from the various portions of said surface, so that a greater heat tends to be conducted; and effecting a relative movement between said heating flames and said surface in a direction longitudinally of said surface. Y

3. A method of heat treating a portion of a metal body, which comprises directing a, group of heating flames against a surface portion of said body, said heating flames having substantially equal individual heating effects and the centers of adjoining heating flames being spaced at increasing distances apart from one end of said group to the other; and effecting a relative movement between said surface and said heating flames.

4. A method of heat treating a.porti0n of a metal body, which comprises directing a group of heating flames against a surface portion of said body, said heating flames having substantially equal individual heating effects and being disposed in at least one row, the distance between centers of adjoining heating flames at one end of a row being greater than at the other end ofsaid row; and effecting a relative movement between said heating flames and said surface.

5. A method of heat treating a gear tooth, comprising directing a group of heating flames against the surface of said tooth, said flames having substantially equal individual heating effects and the distance between centers of adjoining flames increasing from one end of .said group to the other; positioning said flames relatively to said tooth from a point adjacent the root to a point adjacent the top of said tooth, so that the distance between centers of adjoin ing heating flames increases from the root to the top of said tooth and a greater amount of heat is applied to said tooth adjacent the root thanadjacent the top thereof; and applying said group of heating flames to successive surface portions of said tooth across the width thereof.

ROGER 0. DAY. 

